Blood vessels of the mammalian body can be subject to a variety of diseases, traumas, and pathological conditions. In some cases, failure of blood vessels is an aspect of one or more of these conditions. Failure of a blood vessel can involve separation of an inner layer of the blood vessel wall from the remaining outer layers of the blood vessel wall. As the inner layer of blood vessel tissue peels away, a space is formed within the layers of the blood vessel tissue. The space usually fills with blood and expands to form two channels, with the peeled-away tissue residing between the two channels. One of the channels is a remnant of the original blood vessel and continues to function as a blood conduit. This anatomical structure is referred to as the true lumen. The blood-filled space delimiting the other channel is referred to as a false lumen. The delamination of tissue in this manner is referred to as a dissection. The tissue residing between the two lumens, or channels, is referred to as the septum. Dissections involving the portion of the aorta that runs through the thoracic cavity are referred to as thoracic aortic dissections. There are two types of thoracic aortic dissections. The first type of thoracic aortic dissection involves the ascending aorta and is referred to as a Type A dissection according to the Stanford aortic dissection classification system. Type A thoracic aortic dissections most often require immediate surgical intervention. The second type of thoracic aortic dissection does not involve the ascending aorta and is referred to as a Type B dissection as classified by the Stanford system. While some Type B dissections require immediate intervention, most can be medically managed for a time before surgery is required. However, damage to the aorta wall due to a dissection can lead to severe complications and/or death.
The ability to treat Type B thoracic aortic dissections surgically is often limited. When surgery is indicated, the principle surgical method currently employed to correct a Type B thoracic aortic dissection is to access the damaged blood vessel surgically and replace the damaged aorta with a vascular graft. One minimally invasive technique currently used is to cut the septum and extend the cut longitudinally along enough of the length of the dissection to disrupt the false lumen. Once the peeled-away tissue “flap” forming the false lumen is surgically disrupted, blood and other fluids contained in the false lumen by the tissue flap can be cleared and denied a location to recollect. The difficulty in performing surgical cuts of this nature inside such a mechanically and biologically compromised aorta, or other major blood vessel, limits the number of suitable candidates for the surgery.
Minimally invasive techniques may provide alternative approaches to treating dissections. One minimally invasive technique utilizes percutaneous transluminal angioplasty balloons to create multiple fenestrations within a septum. This is accomplished by creating a small hole in the septum using a catheter delivered needle or wire. The balloon is then placed in the hole and inflated to enlarge the hole. Another minimally invasive approach uses a wire introduced into an appropriate blood vessel, most commonly in a leg. The wire is inserted into and navigated through the vasculature to the site of the dissection. The wire is advanced through the septum into the false lumen. Once the wire has been advanced down the aorta, some prescribed length, the wire is brought back into the true lumen via the septum. The leading end of the wire is then grasped with an ancillary instrument and pulled down onto tissue of the septum. This places the wire in contact with the septal tissue where the wire functions as a cutting edge. As the wire is pulled, it cuts through the septum. The cut is extended by continuing to pull on the wire. Once a desired cut in the septum is completed, the leading end of the wire is released from the grasping instrument and the wire removed from the vasculature through the introduction site. Controlling movement, direction, and speed of the wire as the wire propagates the incision in the septum is difficult and often limits this procedure to patients with no other surgical options.
A variety of intravascular cutting tools have been developed to treat a number of pathological conditions, none of which include blood vessel dissections. U.S. Pat. No. 3,704,711, issued to Park, discloses a catheter-based cutting tool for creation of an atrial septal fenestration without thoracotomy. The cutting portion of the tool has a retractable cutting blade confined within a housing. The cutting blade is actuated with a control wire running the length of the catheter. A flexible guidewire is also included with the housing. The flexible guidewire resides above the cutting blade in a retracted configuration and extends to form a loop above the blade when extended. When in an extended configuration, the flexible guidewire is said to provide tactile feedback and assist in locating the cutting tool within a heart. The device may also be sufficiently radiopaque to be visualized with conventional instrumentation. A cut is made in an atrial septum by placing the cutting tool within an atrium with the cutting blade and flexible guidewire in a retracted configuration. Once inside an atrium, the flexible guidewire is extended to form a loop. The loop is used to help a practitioner confirm the location of the cutting tool within an atrium. The flexible guidewire does not assist the cutting blade in contacting or cutting an atrial septum. Once the cutting tool is in a desired location, the control wire is actuated to extend the cutting blade. When the cutting blade has been extended away from its housing, the catheter and housing are withdrawn slightly to bring the cutting blade in contact with septal tissue. As the catheter and housing are withdrawn from an atrium, the extended cutting blade cuts some or all of the atrial septum. Upon completion of a desired septal cut, the cutting blade and flexible guidewire are both retracted into the housing. The housing is then removed from the heart by withdrawing the catheter. If necessary, the procedure can be repeated.
U.S. Pat. No. 5,053,044, issued to Mueller et al., discloses a vascular catheter having a tip with a cutting blade mounted within the tip. The catheter is provided with a mechanism for extending the cutting blade transversely with respect to the catheter when the blade tip is located within a region of stenosis. When the cutting blade is extended, the catheter is moved axially with respect to the catheter so the cutting blade forms an incision in the region of stenosis.
U.S. Pat. No. 5,993,469, issued to McKenzie et al., discloses an arterial catheter system for removing plaque. The catheter system includes an atherectomy assembly. The atherectomy assembly has a mechanism for trapping and holding mobile or fixed plaque and an excising mechanism for removing the plaque. The excising mechanism can include one of several types of rotating cutting blades located within a housing. As the particular cutting blade rotates, plaque protruding into the housing is sheared off and excised from the blood vessel. In some embodiments, rotating cutting blades are provided as single curved blades, cutting blades configured in a twisted helical manner, circular cutting blades, or rotatable cylindrical assemblies having portions removed forming an orifice. As plaque is drawn into the orifice, the cutting blade sweeps across an edge of the orifice opening and excises atheromatous plaque extending through the orifice opening. In another embodiment, a sharpened cylindrical member is initially retained within a housing near an orifice opening to cut plaque. As plaque enters the orifice, the cylindrical cutting blade is advanced toward the distal end of the housing to excise the plaque. In yet another embodiment, a cutting assembly having sharpened movable claws is disclosed. The movable claws are used to enclose, pinch, and cut plaque. Scissor-like cutting blades are also disclosed by McKenzie et al.
McKenzie et al. also disclose an atherectomy catheter equipped with one or more deployable positioning “fingers.” According to McKenzie et al., the deployable positioning fingers act to bias the catheter in the lumen of a blood vessel toward a plaque within a region of interest. The positioning fingers may be mechanically expandable projections or inflatable balloons. The inflatable balloons are said to be inflatable through one or more lumens within the catheter.
None of these devices are designed or intended to treat dissections in vascular structures. Indeed, none of these devices are able to reliably locate and disrupt vascular dissections. A medical cutting tool for treating dissections in vascular structures would require a delivery catheter-based cutting blade assembly with a remotely movable cutting blade combined with one or more expandable displacement elements assisting the placement, contact, support, and operation of the cutting blade. If a procedure were to be implemented to treat dissections involving the creation of a hole in the septum by inserting a medical cutting tool through the hole, a member could be added to the cutting tool to blunt the assembly and assist in locating the assembly in the false lumen. In such a procedure, the cutting tool would be used to cut enough of the dissection to reduce or eliminate the false lumen. In some instances, a prosthetic medical device might be used following the disruption of the septum.